1. Field of the Invention
The present invention relates to a DC motor control system, particularly, it relates to an electrical angle control system for a brushless DC motor to ensure an acceleration characteristic at the start of rotation and to reduce power consumption of the motor.
2. Description of the Related Art
In general, a DC motor has many merits, for example, a rapid start acceleration, a large start torque, a linear characteristic of rotation for the change in a voltage supply, and a linear characteristic of torque for the change in an input current. Accordingly, the DC motor is widely used in various fields, particularly, as a control motor of an automatic control system based on the above merits.
Further, as is known, a brushless DC motor has an electrical rectification (commutation) circuit instead of a mechanical rectification means, for example, a brush and a commutator. Accordingly, the brushless DC motor has a good noise characteristic because it has no contact portions in the rectification mechanism.
Because of a good noise characteristic the brushless DC motor is also used as a spindle motor for a magnetic disc apparatus. In the magnetic disc apparatus, it is also important to reduce power consumption of the spindle motor.